Joule-thomson effect gas liquefier



Aug. 7, 1962 D. K. CQLES ETAL JOULE-THOMSON EFFECT GAS LIQUEFIER FiledFeb. 17, 1959 United States Patent 3,048,021 JOULE-THOMSON EFFECT GASLIQUEFIER Donald K. Coles and Wayne R. Frame, Fort Wayne, Ind.,assignors to International Telephone and Telegraph Corporation FiledFeb. 17, 1959, Ser. No. 793,863 11 Claims. (Cl. 62-36) This inventionrelates generally to cooling devices for providing extremely lowtemperatures and more particularly t-o cooling devices of theJoule-Thomson gas liquefier type.

Joule-Thomson effect cooling devices are well known in the art and areemployed where it is desired to obtain extremely low temperatures;Joule-Thomson effect cooling devices are capable of producingtemperatures as low as -196 C. Such devices conventionally include anelongated, straight thin-wall tube or jacket having a closed lower endand a low pressure gas discharge open 'ing adjacent its other end.Entering the jacket ad acent the low pressure gas discharge end is asmall diameter elongated capillary tube extending downwardly in a coiledcoil configuration, and terminating in a small nozzle adjacent theclosed end of the jacket. Gas having a Joule-Thomson coefiicient whichis positive at room temperature, such as nitrogen, is supplied underhigh pressure to the capillary tube and expands through the nozzle. Thisexpansion of gas from the nozzle causes initial cooling and the gas thenflows upwardly over the convolutions of the capillary tubing, thusextracting further heat from the tubing and the gas flowing downwardlytherein, the gas at reduced pressure being finally exhausted to theatmosphere through the low pressure discharge opening of the jacket.Such Joule-Thomson gas liquefiers (commonly referred to as cryostats)have commonly been employed for cooling infrared cells, typically beinginserted in a cooling well formed as a reentrant tubular portion in theenclosing envelope of the cell.

Prior conventional cryostat devices of the type employing coiled coilcapillary tubes known to the present applicants have been required to beof substantial length in order to provide sutficient'cooling, thislength in turn dictating the over-all length of the infrared cell.Furthermore, prior conventional cryostat constructions have had aserious heat leak along the outer jacket by virtue of its over-alllength and substantial diameter. Furthermore, the long length ofcapillary tubing presently employed in conventional cryostats hasnecessitated a substantial nitrogen flow from a source providingnitrogen at relatively high pressure, e.g., five litres per minute froma two thousand (2000) pounds per square inch source. There arerequirements, however, for infrared cells having substantially shorterlength than prior. cells which in turn necessitates the provision ofsubstantially shorter cryostat devices. However, to the best of thepresent applicants knowledge, all efforts to shorten conventionalcryostat designs by increasing their diameter have resulted in failure,even though the same effective length of capillary tubing was utilized.In addition, it is desirable to provide a cryostat device requiring aconsiderably smaller nitrogen flow than prior cryostat constructions,i.e., two (2) to three (3) litres per minute versus four (4) .to five(5) litresper minute, and an additional requirement that thenitrogenreservoir supply nitrogen at a lower pressure than hasheretofore been 7 possible. a

It is therefore desirable to provide a Joule-Thomson gas liquefier whichwill provide the same cooling elfect as prior devices of thistype, buthaving a substantially shorter length than has heretofore been possible.It is further desirable that such a Joule-Thomson elfect c001 ice 2 ingdevice be capable of fabrication in considerably larger diameters thanhas been found to be possible with prior conventional cryostatconstructions. Furthermore, it is desirable to provide a cryostatconstruction providing the same cooling as provided by priorconstructions employing, however, a substantially smaller nitrogen flowfrom a lower pressure source of gas.

It is therefore an object of our invention to provide an improvedJoule-Thomson gas liquefier.

Another object of our invention is to provide an improvedJ'oule-I'homson gas liquefier providing the same cooling effect in asubstantially shorter length than prior devices of this type.

A further object of this invention is to provide an improvedJoule-Thomson gas liquefier providing the same cooling effect as priordevices of this type with a smaller gas flow and lower gas supplypressure than has heretofore been possible.

Yet another object of our invention is to provide an improvedJoule-Thomson gas liquefier possessing the desirable features enumeratedabove.

Our invention in its broader aspects provides a Joule- Thomson gasliquefier having a first elongated convolute tube having a closed endand a low pressure gas discharge opening adjacent its other end and asecond elongated convol-ute tube positioned in the first tube and having a gas discharge opening at one end adjacent the closed end of thefirst tube and having its other end extending out of the first tubeadjacent the other end thereof and adapted to be connected to a supplyof high pressure gas. In accordance with a preferred embodiment of ourinvention, the inner elongated tube is coiled in a helix substantiallythroughout its length, and is positioned in the first tube in goodthermal contact with the inner wall thereof, the outer tube with theheli'cally coiled inner tube therein being coiled in a helixsubstantially throughout its length.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a view in perspective, partly broken away, illustrating theimproved Joule-Thomson gas liquefier construction of our invention;

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a cross-sectional view similar to FIG. 2 illustrating aslightly modified form of our invention;

FIGS. 4 and 5 are cross-sectional views illustrating another embodimentof our invention; and

FIG. 6 is a cross-sectional view illustrating a further embodiment ofour invention.

Referring now to FIGS. 1 and 2 of the drawings, we have here provided aJoule-Thomson gas'liquefier, gen erally identified as 10 which includesan eflicient and compact heat exchanger with low thermal conductancebetween the two ends thereof. In accordance with our invention, theJoule-Thomson gas liquefier 10 comprises an elongated outer tube orjacket 11 having its end 12 closed,

as by a heliarc weld, and with its other end 13'having a low pressuregas exhaust passageway 14 communicating with the atmsophere, as shown.Positioned within the elongated outer tube 11 is an inner elongatedcapillary tube 15 having a gas discharge nozzle 16 at its lower endadjacent the'clos'ed end .12 of the outer tube 11, and hav- 'ing itsother end 17 extending out of the exhaust passage- I way 14 of the outertube 11, adapted to be connected to and also in the cross-sectional viewof FlG. 2; the elonferred to as counter-current heat exchange. I tion ofthe device has started, the newly entering gas is epaaoar eral timeslarger than the diameter of the outer tube 11,

as shown.

When employed as a Joule-Thomson gas liquefier, high pressure gas, suchas nitrogen, at one hundred atmospheres pressure, is introduced to thehigh pressure end 17 of the inner tube 15. This gas then flowsdownwardly in the convolutions of the inner tube 15 toward the nozzleend 16, the nozzle being preferably somewhat constricted so that asuit-able pressure drop takes place near the nozzle end 16 of the innertube 15. After being exhausted from the nozzle 16 of the inner tube 15,the pressure of the gas is much lower than previously so that the gasthen expands. Associated with this expansion is a cooling effect, knownas the Joule-Thomson effect. By virtue of the provision of the closedend 12 of the outer tube 11, the expanded gas exhausted from the nozzle16 of the inner tube 15' is forced to retrace its path upwardly over theconvolutions of the inner tube 15, extracting heat from the newlyentering gas in the inner tube 15 and being in turn warmed; this mode ofoperation is commonly re- Once operaprecooled and on being exhaustedfrom the nozzle 16 of the inner tube 15, cools itself on expansion to astill lower temperature, finally resulting in the provision of anextrernely low temperature.

'It will now be seen that in contrast with prior conventionalJoule-Thomson gas liquefier constructions in which the expanded gasfollowed -a straight line path upwardly over the convolutions of thecoiled-coil capillary tube, in our improved construction, the expandedgas follows a much longer spiral path, thus increasing the heatexchanging eifect without increasing the over-all length of the device,or on the other hand providing the same heat exchanging eifect with amuch shorter over-all length. In

' addition, it will be observed that the heat leakage along the outerjacket of the prior devices has been reduced through the reduction ofthe diameter of the outer tube or jacket 11 and also by the increase inits spiral length.

In a cryostat device constructed in accordance with our invention, theouter and inner tubes 11 and 15 respectivea ly are preferably formed ofmetal having a comparatively low thermal conductivity, such as stainlesssteel. In the assembly of the device of FIGS. 1 and 2, the inner tube 15is first coiled up in its helically coiled form and is then inserted inthe outer tube 11 which is then in turn coiled I up to provide thehelical configuration shown in MG. 1.

In order to increase the thermal conductance between the Outer tube '11and the inner tube 15, we have found it desirable to copper-plate theinner tube 15 lightly prior to the coiled and plated inner tube 15 isthen wound into the helical form shown, and the resulting assembly isthen heated in a hydrogen furnace until the copper-plating on the innertube 15 forms a braze between the inner and outer tubes 15 and 11.

Refer-ring now briefly to FIG. 3, it will be readily understood that theouter tube 11 may be deformed during the operation of winding it intohelical form so that it is generally elliptical in cross section, asshown, thus grasping theconvolutions of the inner tube 15 more tightlythereby to increase the efliciency of heat exchange.

Referring now to FIGS. 4 and 5, it will be observed that it maybedesirable to provide several inner helically coiled tubes effectivelyconnected in parallel. Thus, in

- FIG. 4, we have shown two inner tubes 15a positioned with outer tube11a; the inner tubes 15a respectively being disposed in side-by-siderelationship, and being in thermal its insertion in the outer tube '11.The outer tube 11 with contact with the inner wall of the outer tube 11aas shown. In FIG. 5, we-have shown the provision or three inner tubes15b, likewise positioned within the outer tube 11b in abuttingside-by-side relationship, and again in thermal contact with the outertube 11b.

Referring now to FIG. 6, it will be observed that the inner tube 150 mayhave a complex helical configuration, as shown, with each successiveconvolution, such as 18, 19 and 20*being in thermal contact with theinner wall of the outer tube 110 at angularly spaced points,

as shown.

In an actual cryostat device constructed in accordance with ourinvention, the heat exchanger length was /1 inch, compared with a lengthof 2 /2 inches in a comparable cryostat of conventional construction.The diameter of the helix of the outer tube 11 of the device inaccordance with our invention was inch with the outer tube '11 having adiameter of .090 inch, compared with an outside diameter of .188 inch inthe case of the prior conventional device; it is thus observed that inaccordance with our invention, it is possible to construct aJoule-Thomson gas liquefier device having a considerably larger over-alloutside diameter than has previously been possible with conventionalconstructions. In the device in accordance with our invention, the outertube 11 had an inside diameter of .070 inch and the inner tube 15 had anoutside diameter of .020 inch and an inside diameter of .010 inch. Withthis device, a temperature of l94 Was obtained, with a nitrogen flow oftwo (2) litres per minute from a source of nitrogen of 1200 pounds persquare inch compared with a nitrogen flow of five (5) litres perrrrinute from a source of nitrogen having a pressure of 1700 pounds persquare inch in the case of a comparable conventional cryostatconstruction. It is thus seen that a much smaller volume of nitrogenfrom a source having a considerably lower pressure is employed with ourimproved cryostat construction.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention.

What is claimed is:

l. A Joule-Thomson gas liquefier comprising: a first elongated convolutetube having a closed end and a low pressure gas discharge openingadjacent its other end; and a second elongated convolute tube positionedin said first tube in contact therewith and having a gas dischargeopening at one end thereof adjacent said closed end of said first tube,the direction of curvature of said second convolute tube being angularlydisposed to the direction of curvature of said first convolute tube,said second tube having its other end extending out of said first tubeadjacent said other end thereof and adapted to be connected to a supplyof high pressure gas.

2. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having a gas dischargeopening at one end thereof, said second tube being coiled in a helixsubstantially throughout its length and being positioned in said firsttube in contact therewith, said second tube having said gas dischargeopening end positioned adjacent said closed end of said first tube andhaving its other end extending out of said first tube adjacent saidother end thereof and adapted to be connected to a supply of highpressure gas; said first tube with said second tube tially smaller thanthe inside diameter of said first tube and having a gas dischargeopening at one end thereof, said second tube being coiled in a helixsubstantially throughout its length and being positioned in said firsttube in thermal contact with the inner wall thereof, said second tubehaving said gas discharge opening end positioned adjacent said closedend of said first tube and having its other end extending out of saidfirst tube adjacent said other end thereof and adapted to be connectedto a supply of high pressure gas; said first tube with said second tubetherein being coiled in a helix substantially throughout its length witha diameter several times greater than the outside diameter of said firsttube, the direction of curvature of said second tube being angularlydisposed to the direction of curvature of said first tube.

- 4. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having an outside diametersubstantially smaller than the inside diameter of said first tube andhaving a gas discharge opening at one end thereof, said second tubebeing coiled in a helix substantially throughout its length with adiameter substantially equal to the inside diameter of said first tube,said second tube being positioned in said first tube in thermal contactwith the inner wall thereof with its gas discharge opening end adjacentsaid closed end of said first tube and its other end extending out ofsaid first tube adjacent said other end thereof and adapted to beconnected to a supply of high pressure gas; said first tube with saidsecond tube therein being coiled in a helix substantially throughout itslength with a diameter several times greater than the outside diameterof said first tube, the direction of curvature of said second tube beingangularly disposed to the direction of curvature of said first tube.

5. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having an outside diametersubstantially smaller than the inside diameter of said first tube andhaving a gas discharge opening at one end thereof, said second tubebeing coiled in a helix substantially throughout its length and beingpositioned in said first tube in thermal contact with the inner wallthereof, said second tube having said gas discharge opening endpositioned adjacent said closed end of said first tube and having itsother end extending out of said first tube adjacent said other endthereof and adapted to be connected to a supply of high pressure gas;said first tube with said second tube therein being coiled in a helixsubstantially throughout its length with a diameter several timesgreater than the outside diameter of said first tube, the direction ofcurvature of said second tube being angularly disposed to the directionof curvature of said first tube; said second tube being brazed to saidinner wall of said first tube.

6. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having an outside diametersubstantially smaller than the inside diameter of said first tube andhaving a gas discharge opening at one end thereof, said second tubebeing coiled in a helix substantially throughout its length and beingpositioned in said first tube in thermal contact with the inner wallthereof, said second tube having said gas discharge opening endpositioned adjacent saidclosed end of said first tube and having itsother end extending out of said first tube adjacent said other endthereof and adapted to be connected to a supply of high pressure gas;said first tube with said second tube therein in being coiled in a helixsubstantially throughout its length with a diameter several timesgreater than the outside diameter of said first tube, the

6 direction of curvature of said second tube being angularly disposed tothe direction of curvature of said first tube; said first and secondtubes being respectively formed of relatively low thermal conductivitymetal, said second tube being plated with a relatively low melting rpoint metal and brazed to said inner Wall of said first tube.

7. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having an outside diametersubstantially smaller than the inside diameter of said first tube andhaving a gas discharge opening at one end thereof, said second'tubebeing coiled in a helix substantially throughout its length and beingpositioned in said first tube in thermal contact with the inner Wallthereof, said second tube having said gas discharge opening endpositioned adjacent said closed end of said first tube and having itsother end extending out of said first tube adjacent said other endthereof and adapted to be connected to a supply of high pressure gas;said first tube with said second tube therein being coiled in a helixsubstantially throughout its length with a diameter several timesgreater than the outside diameter of said first tube, the direction ofcurvature of said second tube being angularly disposed to the directionof curvature of said first tube; said first tube having a generallyelliptical cross-section in its coiled portion and intimately engagingthe coils of said second tube.

3. A Joule-Thomson gas liquefier comprising: an outer elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and at least two inner elongated tubes, each of saidinner tubes having a gas discharge opening at one end thereof and beingcoiled in a helix substantially through its length, said inner tubesbeing positioned in said outer tube with their gas discharge openingends respectively positioned adjacent said closed end of said outer tubeand with their other ends respectively extending out of said outer tubeand adapted to be supplied with high pressure gas; said outer tube withsaid inner tubes therein being coiled in a helix substantiallythroughout its length the direction of curvature of each of said innertubes being angula-rly disposed to the direction of curvature of saidouter tube.

9. A ioule fhomson gas liquefier comprising: an outer elongated tubehaving a closed end and a low pressure gas dischar e opening adjacentits other end; and at least two inner elongated tubes, each of saidinner tubes having a gas discharge opening at one end thereof and beingcoiled in a helix substantially throughout its length, said inner tubesbeing positioned in said outer tube in side-byside abutting relationshipand respectively in thermal contact with the inner wall of said outertube, said inner tubes having their gas discharge ends respectivelypositioned adjacent said closed end of said outer tube and having theirother ends respectively extending out of said outer tube and adapted tobe supplied with high pressure gas; said outer tube with said innertubes thereon being coiled in a helix substantially throughout itslength the direction of curvature of each of said inner tubes beingangularly disposed to the direction of curvature of said outer tube.

10. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having an outside diametersubstantially smaller than the inside diameter of said first tube andhaving a gas discharge opening at one end thereof, said second tubebeing coiled in simple helix substantially throughout its length andbeing positioned in said first tube in thermal contact with the innerWall thereof, said second tube having said gas discharge opening endpositioned adjacent said closed end of said first tube and having itsother end extending out of said first tube adjacent said other endthereof and adapted to be connected to a supply of high pressure gas;said first tube with said second tube therein being coiled in a simplehelix substantially throughout its length, the direction of curvature ofsaid second tube being angularly disposed to the direction of curvatureof said first tube.

11. A Joule-Thomson gas liquefier comprising: a first elongated tubehaving a closed end and a low pressure gas discharge opening adjacentits other end; and a second elongated tube having an outside diametersubstantially smaller than the inside diameter of said first tube andhaving a gas discharge opening at one end thereof, said second tubebeing coiled in a complex helix substantially throughout its length,said second tube being positioned in said first tube with eachconvolution of said second tube having a portion in thermal contact withthe inner wall of said first tube, said second tube having said gasdischarge opening end positioned adjacent said closed end of said firsttube and having its other end extending out of said first tube adjacentsaid other end thereof and adapted to be connected to a supply of highpressure gas; said first tube with said second tube therein 8 beingcoiled in a simple helix substantially throughout its length, thedirection of curvature of said second tube being angularly disposed tothe direction of curvature of said first tube.

References Cited in the file of this patent UNITED STATES PATENTS

